1. Field of the Invention
The present invention relates to a fixed constant velocity universal joint for use in automobiles and various industrial machines and, more particularly, to a fixed constant velocity universal joint using eight balls as torque transmitting elements.
2. Description of the Background Art
Constant velocity universal joints are classified into fixed joints which cannot slide and sliding or plunging joints which can slide in the axial direction thereof. FIGS. 14 and 15 show a Rzeppa constant velocity universal joint (hereinafter referred to as BJ-type) as a typical fixed constant velocity universal joint. This fixed constant velocity universal joint is comprised of an outer ring 1 as an outer joint member having six axially extending arcuate ball grooves 1b formed in a spherical inner surface 1a thereof, an inner ring 2 as an inner joint member having six axially extending arcuate ball grooves 2b formed in a spherical outer surface 2a thereof, six balls 3 as torque transmitting elements arranged between the ball grooves 1b of the outer ring 1 and the ball grooves 2b of the inner ring 2, and a cage 4 holding the balls 3.
Centers P and Q of the ball grooves 1b and 2b, respectively, are axially offset from a joint center O by the same distance (PO=QO) on either side of the center O. That is, the center P of the ball grooves 1b of the outer ring 1 is offset on the opening side of the outer ring 1 from the center O of the spherical inner surface 1a by the distance PO. The center Q of the ball grooves 2b of the inner ring 2 is offset on the inner side of the outer ring 1 from the center O of the spherical outer surface 2a by the distance QO. The centers of the inner surface 1a of the outer ring 1 and the outer surface 2a of the inner ring 2 are matched with the joint center O.
One of shafts to be coupled (not shown) is connected to the outer ring 1 and the other, shaft 5, is connected to the inner ring 2. Thus, the inner ring 2 has a serrated or splined hole 2c for engagement with a serrated or splined part of the shaft 5. When the axes of the outer ring 1 and the inner ring 2 form an angle (operating angle of the joint), the balls 3 are retained by the cage 4 within a plane perpendicular to a bisector of the operating angle, thereby ensuring a constant angular velocity of the inner and outer rings.
In the fixed constant velocity universal joint using eight balls, the internal design is optimized to ensure the same durability and strength as a fixed constant velocity universal joint using six balls. See Japanese unexamined patent documents H9-177814, 2003-4062, and 2003-307235.